In general, a planetary gear is used for an automatic transmission mounted on an automobile and other vehicles, and comprises a carrier having a plurality of pinion gears, a sun gear positioned at the center of the planetary gear and held in mesh with the pinion gears, and a ring gear positioned to surround the sun gear and held in mesh with the pinion gears. The carrier has two carrier plates. One of the carrier plates has a plurality of connection elements mounted thereon. The connection elements are bent and have respective outwardly projected end portions thereof connected to the other of the carrier plates to ensure that the two carrier plates support the axial end portions of a plurality of pinion shafts rotatably supporting the pinion gears. The carrier plates, the pinion shafts, and the pinion gears constitute as a whole a carrier assembly.
The conventional carrier assembly of this kind so far known is shown in FIG. 6. FIG. 6 is a cross sectional view of a carrier assembly forming part of a planetary gear to be used for an automatic transmission to be mounted on an automobile. In FIG. 6, a first carrier plate 51 is mounted on one end portion of an input shaft 52 drivably connected to an engine not shown. The first carrier plate 51 has a radially inner portion formed with a plurality of first shaft holes 51a equally spaced apart from one another in the circumferential direction of the first carrier plate.
The first carrier plate 51 is positioned in opposing relationship with a second carrier plate 53 which has a radially inner portion formed with a plurality of second shaft holes 53a in opposing relationship with the respective first shaft holes 51a. 
Between the first shaft holes 51a and the second shaft holes 53a opposing to one another, there are pinion shafts 54. The pinion shafts 54 have pinion gears 55 each rotatably mounted thereon, the pinion gears 55 being held in mesh with a sun gear 56 shown by phantom lines in FIG. 7.
FIGS. 8A and 8B respectively show the first carrier plate 51 and the second carrier plate 53 pressed and shaped by a press working. As shown in FIG. 8B, the second carrier plate 53 has a radially outer peripheral portion formed with a plurality of connection elements 57, each projecting radially outwardly of the second carrier plate 53. In FIG. 8B, reference numeral 57a indicates a base portion forming part of each of the connection elements 57.
The above carrier assembly is assembled in such a manner that the connection elements 57 of the second carrier plate 53 are bent toward the first carrier plate 51 to weld and fix the respective outwardly projected end portions 57b of the connection elements 57 with the radially outer peripheral portion of the first carrier plate 51. In this manner, the first carrier plate 51 and the second carrier plate 53 are connected with each other with each of the connection elements 57 being circumferentially interposed between the pinion gears 55 (for example see Patent Document 1).
Patent Document 1: Japanese Patent Publication No. 2007-139061